Atrial fibrillation is a common cardiac arrhythmia and a major cause of stroke. Atrial fibrillation results in a fast and irregular cardiac rhythm which often leads to palpitations and a deterioration of cardiac function with cardiac output decreasing by an average of 30%. There is also an increased incidence of intra cardiac thrombosis (blood clotting and coagulation) which can potentially lead to embolic events such as strokes. Consequently, 20 to 35% of cerebrovascular accidents (CVAs) are related to paroxysmal or chronic atrial fibrillation
This condition is perpetuated by reentrant wavelets propagating in an abnormal atrial-tissue substrate. Various approaches, including electroanatomical and pulmonary vein isolation, have been developed to treat atrial fibrillation.
When the heart is viewed from the back, the most obvious structure lying in the coronary sulcus is the coronary sinus. This sinus receives most of the venous blood from the heart and empties the blood into the right atrium. Its tributaries are the small cardiac vein, the middle cardiac vein and the greater cardiac vein. Internal structures of the right atrium include the coronary sinus opening which may have small valve leaflets.
Difficulties in performing procedures within the coronary sinus include finding the ostium to the coronary sinus, preventing the catheter from slipping out of the coronary sinus and stabilizing the catheter in the coronary sinus in a beating heart. The catheter tends to slip out of the coronary sinus because of ante grade flow and movement of the heart and diaphragm. Moreover, the size and diameter of the coronary sinus can vary greatly between individuals and along the length of any one coronary sinus. Accordingly, significant disadvantages exist with current electrophysiological catheters ability to locate and work in the coronary sinus.
Where mapping of the heart is performed by means of electromagnetic sensing, the patient is placed in a magnetic field generated, for example, by situating under the patient a pad containing coils for generating a magnetic field. A reference electromagnetic sensor is fixed relative to the patient, e.g., taped to the patient's back, and a catheter containing a second electromagnetic sensor is advanced into the patient's heart. Each sensor comprises three small coils that in the magnetic field generate weak electrical signals indicative of their position in the magnetic field. Signals generated by both the fixed reference sensor and the second sensor in the heart are amplified and transmitted to a computer that analyzes the signals and then displays the signals on a monitor. By this method, the location of the sensor in the catheter relative to the reference sensor can be ascertained and visually displayed. Although the reference sensor is generally positioned outside the patient's body, it is also desirable for certain applications to position the reference sensor in the patient's heart, in particular, in or near the coronary sinus. Because the reference sensor serves as a reference location for the second electromagnetic sensor, movement of the reference sensor in or near the coronary sinus should preferably be minimized.